I figured that I should update for everyone. Well, we had two problems. The first is that someone at some point of time pulled the O2 sensor's heater fuse & never put one back in.

However, the 3 flashing issue was because someone also just straight up removed a light from the dash pod. The neutral light was still good. However, we could tell that at one point there was a light in one of the other holes that had no display due to the contacts having been rubbed clean. On a whim, we threw one in & it fixed it. I guess that person thought it was a spare.